2 * Copyright 1995-2018 The OpenSSL Project Authors. All Rights Reserved.
4 * Licensed under the OpenSSL license (the "License"). You may not use
5 * this file except in compliance with the License. You can obtain a copy
6 * in the file LICENSE in the source distribution or at
7 * https://www.openssl.org/source/license.html
11 #include "internal/cryptlib.h"
12 #include <openssl/bn.h>
13 #include <openssl/sha.h>
15 #include <openssl/asn1.h>
17 static DSA_SIG *dsa_do_sign(const unsigned char *dgst, int dlen, DSA *dsa);
18 static int dsa_sign_setup_no_digest(DSA *dsa, BN_CTX *ctx_in, BIGNUM **kinvp,
20 static int dsa_sign_setup(DSA *dsa, BN_CTX *ctx_in, BIGNUM **kinvp,
21 BIGNUM **rp, const unsigned char *dgst, int dlen);
22 static int dsa_do_verify(const unsigned char *dgst, int dgst_len,
23 DSA_SIG *sig, DSA *dsa);
24 static int dsa_init(DSA *dsa);
25 static int dsa_finish(DSA *dsa);
26 static BIGNUM *dsa_mod_inverse_fermat(const BIGNUM *k, const BIGNUM *q,
29 static DSA_METHOD openssl_dsa_meth = {
32 dsa_sign_setup_no_digest,
34 NULL, /* dsa_mod_exp, */
35 NULL, /* dsa_bn_mod_exp, */
44 static const DSA_METHOD *default_DSA_method = &openssl_dsa_meth;
46 void DSA_set_default_method(const DSA_METHOD *meth)
48 default_DSA_method = meth;
51 const DSA_METHOD *DSA_get_default_method(void)
53 return default_DSA_method;
56 const DSA_METHOD *DSA_OpenSSL(void)
58 return &openssl_dsa_meth;
61 static DSA_SIG *dsa_do_sign(const unsigned char *dgst, int dlen, DSA *dsa)
64 BIGNUM *m, *blind, *blindm, *tmp;
66 int reason = ERR_R_BN_LIB;
70 if (dsa->p == NULL || dsa->q == NULL || dsa->g == NULL) {
71 reason = DSA_R_MISSING_PARAMETERS;
80 if (ret->r == NULL || ret->s == NULL)
87 blind = BN_CTX_get(ctx);
88 blindm = BN_CTX_get(ctx);
89 tmp = BN_CTX_get(ctx);
94 if (!dsa_sign_setup(dsa, ctx, &kinv, &ret->r, dgst, dlen))
97 if (dlen > BN_num_bytes(dsa->q))
99 * if the digest length is greater than the size of q use the
100 * BN_num_bits(dsa->q) leftmost bits of the digest, see fips 186-3,
103 dlen = BN_num_bytes(dsa->q);
104 if (BN_bin2bn(dgst, dlen, m) == NULL)
108 * The normal signature calculation is:
110 * s := k^-1 * (m + r * priv_key) mod q
112 * We will blind this to protect against side channel attacks
114 * s := blind^-1 * k^-1 * (blind * m + blind * r * priv_key) mod q
117 /* Generate a blinding value */
119 if (!BN_priv_rand(blind, BN_num_bits(dsa->q) - 1,
120 BN_RAND_TOP_ANY, BN_RAND_BOTTOM_ANY))
122 } while (BN_is_zero(blind));
123 BN_set_flags(blind, BN_FLG_CONSTTIME);
124 BN_set_flags(blindm, BN_FLG_CONSTTIME);
125 BN_set_flags(tmp, BN_FLG_CONSTTIME);
127 /* tmp := blind * priv_key * r mod q */
128 if (!BN_mod_mul(tmp, blind, dsa->priv_key, dsa->q, ctx))
130 if (!BN_mod_mul(tmp, tmp, ret->r, dsa->q, ctx))
133 /* blindm := blind * m mod q */
134 if (!BN_mod_mul(blindm, blind, m, dsa->q, ctx))
137 /* s : = (blind * priv_key * r) + (blind * m) mod q */
138 if (!BN_mod_add_quick(ret->s, tmp, blindm, dsa->q))
141 /* s := s * k^-1 mod q */
142 if (!BN_mod_mul(ret->s, ret->s, kinv, dsa->q, ctx))
145 /* s:= s * blind^-1 mod q */
146 if (BN_mod_inverse(blind, blind, dsa->q, ctx) == NULL)
148 if (!BN_mod_mul(ret->s, ret->s, blind, dsa->q, ctx))
152 * Redo if r or s is zero as required by FIPS 186-3: this is very
155 if (BN_is_zero(ret->r) || BN_is_zero(ret->s))
162 DSAerr(DSA_F_DSA_DO_SIGN, reason);
171 static int dsa_sign_setup_no_digest(DSA *dsa, BN_CTX *ctx_in,
172 BIGNUM **kinvp, BIGNUM **rp)
174 return dsa_sign_setup(dsa, ctx_in, kinvp, rp, NULL, 0);
177 static int dsa_sign_setup(DSA *dsa, BN_CTX *ctx_in,
178 BIGNUM **kinvp, BIGNUM **rp,
179 const unsigned char *dgst, int dlen)
182 BIGNUM *k, *kinv = NULL, *r = *rp;
187 if (!dsa->p || !dsa->q || !dsa->g) {
188 DSAerr(DSA_F_DSA_SIGN_SETUP, DSA_R_MISSING_PARAMETERS);
195 if (k == NULL || l == NULL || m == NULL)
198 if (ctx_in == NULL) {
199 if ((ctx = BN_CTX_new()) == NULL)
204 /* Preallocate space */
205 q_bits = BN_num_bits(dsa->q);
206 if (!BN_set_bit(k, q_bits)
207 || !BN_set_bit(l, q_bits)
208 || !BN_set_bit(m, q_bits))
215 * We calculate k from SHA512(private_key + H(message) + random).
216 * This protects the private key from a weak PRNG.
218 if (!BN_generate_dsa_nonce(k, dsa->q, dsa->priv_key, dgst,
221 } else if (!BN_priv_rand_range(k, dsa->q))
223 } while (BN_is_zero(k));
225 BN_set_flags(k, BN_FLG_CONSTTIME);
227 if (dsa->flags & DSA_FLAG_CACHE_MONT_P) {
228 if (!BN_MONT_CTX_set_locked(&dsa->method_mont_p,
229 dsa->lock, dsa->p, ctx))
233 /* Compute r = (g^k mod p) mod q */
236 * We do not want timing information to leak the length of k, so we
237 * compute G^k using an equivalent scalar of fixed bit-length.
239 * We unconditionally perform both of these additions to prevent a
240 * small timing information leakage. We then choose the sum that is
241 * one bit longer than the modulus.
243 * TODO: revisit the BN_copy aiming for a memory access agnostic
246 if (!BN_add(l, k, dsa->q)
247 || !BN_add(m, l, dsa->q)
248 || !BN_copy(k, BN_num_bits(l) > q_bits ? l : m))
251 if ((dsa)->meth->bn_mod_exp != NULL) {
252 if (!dsa->meth->bn_mod_exp(dsa, r, dsa->g, k, dsa->p, ctx,
256 if (!BN_mod_exp_mont(r, dsa->g, k, dsa->p, ctx, dsa->method_mont_p))
260 if (!BN_mod(r, r, dsa->q, ctx))
263 /* Compute part of 's = inv(k) (m + xr) mod q' */
264 if ((kinv = dsa_mod_inverse_fermat(k, dsa->q, ctx)) == NULL)
267 BN_clear_free(*kinvp);
273 DSAerr(DSA_F_DSA_SIGN_SETUP, ERR_R_BN_LIB);
282 static int dsa_do_verify(const unsigned char *dgst, int dgst_len,
283 DSA_SIG *sig, DSA *dsa)
286 BIGNUM *u1, *u2, *t1;
287 BN_MONT_CTX *mont = NULL;
290 if (!dsa->p || !dsa->q || !dsa->g) {
291 DSAerr(DSA_F_DSA_DO_VERIFY, DSA_R_MISSING_PARAMETERS);
295 i = BN_num_bits(dsa->q);
296 /* fips 186-3 allows only different sizes for q */
297 if (i != 160 && i != 224 && i != 256) {
298 DSAerr(DSA_F_DSA_DO_VERIFY, DSA_R_BAD_Q_VALUE);
302 if (BN_num_bits(dsa->p) > OPENSSL_DSA_MAX_MODULUS_BITS) {
303 DSAerr(DSA_F_DSA_DO_VERIFY, DSA_R_MODULUS_TOO_LARGE);
310 if (u1 == NULL || u2 == NULL || t1 == NULL || ctx == NULL)
313 DSA_SIG_get0(sig, &r, &s);
315 if (BN_is_zero(r) || BN_is_negative(r) ||
316 BN_ucmp(r, dsa->q) >= 0) {
320 if (BN_is_zero(s) || BN_is_negative(s) ||
321 BN_ucmp(s, dsa->q) >= 0) {
327 * Calculate W = inv(S) mod Q save W in u2
329 if ((BN_mod_inverse(u2, s, dsa->q, ctx)) == NULL)
333 if (dgst_len > (i >> 3))
335 * if the digest length is greater than the size of q use the
336 * BN_num_bits(dsa->q) leftmost bits of the digest, see fips 186-3,
340 if (BN_bin2bn(dgst, dgst_len, u1) == NULL)
343 /* u1 = M * w mod q */
344 if (!BN_mod_mul(u1, u1, u2, dsa->q, ctx))
347 /* u2 = r * w mod q */
348 if (!BN_mod_mul(u2, r, u2, dsa->q, ctx))
351 if (dsa->flags & DSA_FLAG_CACHE_MONT_P) {
352 mont = BN_MONT_CTX_set_locked(&dsa->method_mont_p,
353 dsa->lock, dsa->p, ctx);
358 if (dsa->meth->dsa_mod_exp != NULL) {
359 if (!dsa->meth->dsa_mod_exp(dsa, t1, dsa->g, u1, dsa->pub_key, u2,
363 if (!BN_mod_exp2_mont(t1, dsa->g, u1, dsa->pub_key, u2, dsa->p, ctx,
368 /* let u1 = u1 mod q */
369 if (!BN_mod(u1, t1, dsa->q, ctx))
373 * V is now in u1. If the signature is correct, it will be equal to R.
375 ret = (BN_ucmp(u1, r) == 0);
379 DSAerr(DSA_F_DSA_DO_VERIFY, ERR_R_BN_LIB);
387 static int dsa_init(DSA *dsa)
389 dsa->flags |= DSA_FLAG_CACHE_MONT_P;
393 static int dsa_finish(DSA *dsa)
395 BN_MONT_CTX_free(dsa->method_mont_p);
400 * Compute the inverse of k modulo q.
401 * Since q is prime, Fermat's Little Theorem applies, which reduces this to
402 * mod-exp operation. Both the exponent and modulus are public information
403 * so a mod-exp that doesn't leak the base is sufficient. A newly allocated
404 * BIGNUM is returned which the caller must free.
406 static BIGNUM *dsa_mod_inverse_fermat(const BIGNUM *k, const BIGNUM *q,
412 if ((r = BN_new()) == NULL)
416 if ((e = BN_CTX_get(ctx)) != NULL
419 && BN_mod_exp_mont(r, k, e, q, ctx, NULL))